1. Field of the Invention
The present invention relates to a light source unit and a projector which includes the light source unit.
2. Description of the Related Art
In these days, data projectors are used on many occasions as image projection apparatuses which project images including images of screens and video images of personal computers, as well as images based on image data which is stored in memory cards on to a screen. These projectors are such that light emitted from a light source is collected to a micromirror device called DMD (Digital Micromirror Device) or a liquid crystal plate for display of a color image onto the screen.
Conventionally, projectors have constituted the mainstream of projectors of the type described above which use a high-intensity discharge lamp which emits white light as a light source and in which a color image is projected by coloring the white light so emitted by a color wheel. However, with the projectors in which the white light is colored by the color wheel, since only light of a predetermined wavelength band is extracted from the white light for projection, there is caused a problem that the utilization efficiency of a pencil of light or light rays which are emitted from the light source is low. In addition, there is also a problem that the life of high-intensity discharge lamps is short.
To cope with these problems, in recent years, there have been made many developments and proposals on projectors which use, as a light source, a light emitting diode (LED), a laser diode (LD) or a solid light emitting device (a semiconductor light emitting device) such as a device utilizing organic EL technology. For example, Japanese Unexamined Patent Publication No. 2004-341105 (JP-A-2004-341105) proposes a light source unit which includes a luminescent wheel in which a luminescent material layer or layers are laid in a circumferential direction on a transparent disk and an ultraviolet radiation emitting diode which functions as a semiconductor light emitting device. The light source of the proposal in JP-A-2004-341105 is configured so that ultraviolet radiation is shone onto the luminescent wheel from a rear surface side thereof as excitation light so as for luminescent light to be emitted from a front surface side of the luminescent wheel for use as light source light.
In the invention described in JP-A-2004-341105, a red luminescent material, a green luminescent material and a blue luminescent material are exited by the ultraviolet radiation, and luminescent light rays which are emitted from the luminescent materials are reflected by a digital mircromirror device whose mirrors are switched between ON and OFF so that light rays reflected by the mirrors in the “on” position produce an image. Consequently, compared with the case in which white light emitted from the discharge lamp is colored by the color wheel, the utilization efficiency of light rays emitted from the light source can be enhanced.
In the projector, however, since the luminescent materials of the three colors are laid from end to end in the circumferential direction of the luminescent wheel with the excitation light kept shone onto the luminescent wheel, the luminescent materials are heated to reduce the luminous efficiency thereof, leading to a problem that unevenness in luminance is produced in red, green and blue luminescent light rays and therefore, a high-quality image cannot be projected. In addition, there has been a problem that the luminance and color saturation of the red, green and blue luminescent light rays differ color by color and the colors that are attempted to be projected cannot be reproduced. Further, since the excitation light source is kept turned on at all times, the aging deterioration of the excitation light source is promoted, and the product life of the projector is shortened.